Whole genome sequencing of the model white rot basidiomycete Phanerochaete chrysosporium has revealed the largest P450 contingent known to date in fungi, along with related phase I and phase II metabolic genes and signaling cascade genes. As a part of their functional characterization, genome-wide expression profiling under physiologically distinct conditions, nutrient-limited (ligninolytic) and nutrient-rich (non-ligninolytic), was investigated using a custom-designed 70-mer oligonucleotide microarray developed based on 190 target genes and 23 control genes. All 150 P450 genes were found to be expressible under the test conditions, with 27 genes showing differential expression based on a >twofold arbitrary cut-off limit. Of these, 23 P450 genes were upregulated (twofold to ninefold) in defined high-nitrogen cultures whereas four genes were upregulated (twofold to twentyfold) in defined low-nitrogen cultures. Furthermore, tandem P450 member genes in ten of the 16 P450 genomic clusters showed nonassortative regulation of expression reflecting their functional diversity. Full-length cDNAs for two of the high-nitrogen upregulated genes pc-hn1 (CYP5035A1) and pc-hn2 (CYP5036A1) and partial cDNA for a low-nitrogen upregulated gene pc-ln1 (CYP5037A1) were cloned and characterized. The study provided first molecular evidence for the presence of active components of the cAMP- and MAP kinase-signaling pathways in a white rot fungus; four of these components (cpka and ste-12 of cAMP pathway and two MAP kinases, mps1 and sps1) were significantly upregulated (fourfold to eightfold) under nutrient-limited conditions, implying their likely role in the regulation of gene expression involved in secondary metabolism and biodegradation processes under these conditions.